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PCV, etc

From: Hank Dozier
Email: dozierhc <at> aol.com
Remote Name: 192.75.238.205
Date: December 12, 2003

Comments

A 392 has approximately the same volumetric flow per cylinder stroke as a 400 CID "B" block Mopar engine. I would get a valve from that application and use it. Also, the best place to pull PCV flow from is the valley cover, where the old road draft tube was located. Put a grommet there and place the valve into it, and then run a line to the rear of the carb (WCFB or AFB), or to the PCV port on the front of a Holley. Make sure you have a good clean open oli fill/breather so that the PCV gases are not restricted to the carb. Regarding the loping (looping) idle, this is most likely caused by the carburetors transfer ports being slightly exposed at idle to the engine vacuum. These are the slots ABOVE the idle screw holes in the throttle base plate. Couple of cures to try here. First, set your base timing to something reasonable, like 6 degrees BTC static, carefully turn the idle mixture screw in until they bottom without forcing them, back them both out about 2 1/2 turns, start the engine, and with the engine fully warmed up, set your base idle to 750 rpm or so with NO vacuum to the distributor. Then remove the carb and look/measure to see if the transfer slots are still above the throttle blades. If so, reattach the carb and while still running at idle, put a vacuum on the spark port. You should see no vacuum or very low vacuum (close to atmospheric). If this is the case, then attach the distributor vacuum line, and do a final mixture set by screwing in the idle screws until the engine rpm changes, and backing back out until rpm increases again, plus a 1/4 turn each. IF you have either transfer slots or vacuum advance port exposed, then you will need to move them up. This can be done (carefully) by using something like Devcon aluminum epoxy to fill the lower part of the slot, and a jewelers' file to cut the slot higher by the same amount. The distributor vacuum hole can be drilled with a similar sized drill higher, and the old hole plugged. Try and stay away from using manifold vacuum to the distributor, as this can also cause a rolling idle.

 

Last changed: May 04, 2010